The major objectives of this research proposal are to isolate tuberculin-active products possessing greater specificity and sensitivity than are currently available for use as possible skin test agents from purified protein derivatives (PPD) sensitins of selected mycobacteria. These will be characterized both chemically and physico- chemically in order to compare and relate specific properties to possible biological effects in sensitized and non-sensitized cellular environments. By using in vitro techniques and employing these isolates in various test systems, it is expected that specific cellular events can be correlated and cellular mechanisms unique to delayed hypersensitivity and immunity to tuberculosis can be more clearly defined.